IBBQ-4T - Only port 4 working; all probes work on port 4

The unit is 2 years old. Suddenly stopped working on ports 1-3. Battery fully charged. I have the app but never use it.

Sorry to hear that.
Please make sure the probes are plugged in tightly.
If the probes all work on port 4 but not on ports 1-3, there may be a problem with the ports.
Please kindly understand that the warranty period of IBBQ-4T is one year. Perhaps you can contact support@inkbird.com by email? Maybe they can provide you with some after-sales solutions.